The condensation of tert-butoxycarbonyl-L-alanine (I) with benzyl D-isoglutaminate (II) by means of N-hydroxysuccinimide (NOHS) and dicyclohexylcarbodiimide (DCC) gives the protected dipeptide (III), which is hydrogenated with H2 over Pd/C in methanol yielding tert-butoxycarbonyl-D-isoglutaminyl-L-alanine (IV). The condensation of (IV) with Nepsilon-(benzyloxycarbonyl)-L-lysine benzyl ester (V) by means of ethyl chloroformate and triethylamine affords the protected tripeptide (VI), which is treated with trifluoroacetic acid (TFA) to afford L-alanyl-D-isoglutaminyl-(Nepsilon-benzyloxycarbonyl)-L-lysine benzyl ester (VII).
The condensation of (VII) with 1-O-benzyl-4,6-O-benzylidene-N-acetylmuramic acid (VIII) by means of NOHS and DCC as before gives the protected muramyl tripeptide (IX) , which is treated with acetic acid yielding the partially protected compound (X).
Hydrogenation of (X) with H2 over Pd/C in acetic acid affords Nalpha-(N-acetylmuramoyl-L-alanyl-D-isoglutaminyl)-L-lysine (XI), which is finally condensed with N-hydroxynorbornene-2,3-dicarboxyimide ester of stearic acid (XII) by means of N-methylmorpholine in DMF.